A comparison was made of computation results for molecular weight, critical temperature, critical pressure and the acentric factor for 98 pure components using different methods frequently utilised for pseudocomponents characterising crude oil and petroleum fractions. It is shown that these methods mostly afford the estimated parameters with large errors. On the example of the true boiling point characterisation test, the possibility to use real components instead of pseudo-components is shown. For real components, all thermodynamic characteristics are known with high accuracy. In addition, by the choice of real components, the user can take into account some specificities in the composition of the studied mixture.